Suppression of magnetic instability in inductive recording heads

Abstract

Circuitry for eliminating magnetic instability of an inductive magnetic transducer during sensing of data from a magnetic recording medium to prevent distortion of the readback signal by hysterically moving domain walls. An inductive sensing coil has an impedance constituting the output impedance of the transducer. Means connected to the coil amplifies a data signal generated by the magnetic flux changes and produces a selected input impedance. The sum of these input and output impedances is selected to be small enough to substantially eliminate motion of the domain walls in the yoke of the transducer while the transducer is sensing data from the medium.

We claim: 
     
       1. For use with a magnetic recording medium, circuitry comprising: an inductive magnetic transducer (10) having (i) a yoke region (12) with magnetic domain walls separating differently oriented magnetic domains and (ii) and inductive sensing coil (14) for sensing data on the recording medium and generating a data signal produced by magnetic flux changes, said coil having an impedance constituting the output impedance (Z h ) of the transducer; and   means (22) connected to the coil for amplifying the data signal and having as an input an electronics input impedance (Z in ), where Z in  =-Z h  (1-ε) and ε has a value between +1 and -1, the vectorial sum of said input and output impedances having a magnitude that (i) inhibits motion of the domain walls in the yoke region, while the transducer is sensing data, and (ii) inhibits flux variations of the data signal at frequencies at which motion of the domain walls can occur.   
     
     
       2. The circuitry of claim 1, wherein the value of ε is +1 and the input impedance is zero to short circuit the coil for preventing motion of the domain walls. 
     
     
       3. The circuitry of claim 1, wherein ε is substantially zero and the input impedance therefore is substantially equal to the output impedance, but of a polarity opposite that of the output impedance, thereby to substantially eliminate motion of the domain walls while the transducer is sensing data. 
     
     
       4. The circuitry of claim 1, wherein said means includes a voltage amplifier (24) whose inputs are connected to the coil; and   means (26) shunting the amplifier and providing a negative feedback path across the amplifier for reducing the input impedance substantially to zero.   
     
     
       5. The circuitry of claim 1, wherein said means includes a voltage amplifier (24) whose inputs are connected to the coil; and   a transconductance amplifier (28) in a feedback path from the voltage amplifier providing a negative feedback for reducing the input impedance substantially to zero.   
     
     
       6. The circuitry of claim 1, wherein said means includes a voltage amplifier (30) whose inputs are connected to the coil; and   means (32) shunting the amplifier and providing an impedance (Z fb ) in a positive feedback path that modifies the input impedance (Z in ) to become substantially equal to, but of a polarity opposite that of, the output impedance (Z h ).   
     
     
       7. The circuitry of claim 6, wherein the impedance Z fh  =Z h  (1-ε)(A-1), A being the voltage amplifier gain. 
     
     
       8. The circuitry of claim 1, wherein said means includes a voltage amplifier (30) whose inputs are connected to the coil; and   a transconductance amplifier (34) in a feedback path from the voltage amplifier that provides positive feedback for modifying the input impedance (Z in ) to become equal to, but of a polarity opposite that of, the output impedance (Z h ).   
     
     
       9. The circuitry of claim 8, where the transconductance amplifier (34) has a gain g=1/AZ h  (1-ε), A being the amplification of the voltage amplifier. 
     
     
       10. The circuitry of claim 8, where the transconductance amplifier (34) consists of two transconductance amplifiers (g 1 ,g 2 ) circuited in cascade with an impedance Z to give a transconductance gain g=g 1  g 2  Z, where Z=1/g 1  g 2  AZ h  (1-ε), A being the amplification of the voltage amplifier. 
     
     
       11. A method of inhibiting motion of the magnetic domain walls of the yoke region of an inductive magnetic transducer that includes an inductive sensing coil that senses data on a magnetic recording medium, generates a data signal from magnetic flux changes, and has an impedance constituting the output impedance (Z h ) of the transducer, comprising the steps of: amplifying the data signal with a circuit including an amplifier connected to the coil and having as an input a selectable electronics input impedance (Z in ); and   selecting input and output impedances such that Z in  =-Z h  (1-ε), where ε has a value between +1 and -1 and the vectorial sum of said impedances has a magnitude that (i) inhibits said motion of the domain walls in the yoke region, while the transducer is sensing data, and (ii) inhibits flux variations of the data signal at frequencies at which motion of the domain walls can occur.   
     
     
       12. The method claim 11, including during the selecting step, selecting zero as the magnitude of the input impedance for short circuiting the coil. 
     
     
       13. The method of claim 11, including during the selecting step, selecting substantially zero as the value of ε for causing the magnitude of the input impedance to be substantially equal to, but of a polarity opposite that of, the output impedance.